(i) Field of the Invention
The present invention relates to a method for preparing 2,3-dichloro-1-propanol and 3-chloro-1-propanol.
More specifically, the present invention relates to a method for preparing 2,3-dichloro-1-propanol and 3-chloro-1-propanol by hydroxymethylating 1,2-dichloroethane with methanol. These products are industrially important in themselves or as intermediates of reactions.
(ii) Description of the Prior Art
Since 2,3-dichloro-1-propanol can easily be converted into epichlorohydrin with a caustic alkali or milk of lime, it is useful as a precursor of epichlorohydrin which is a raw material of an epoxy resin and a synthetic rubber. On the other hand, 3-chloro-1-propanol is also a useful substance and industrially important as an intermediate for a reaction.
Nowadays, 2,3-dichloro-1-propanol which is the precursor of epichlorohydrin can be industrially manufactured by a method which comprises chlorinating propylene at a high temperature to form allyl chloride, and then treating allyl chloride with chlorine and water to form a chlorohydrin, or a method which comprises acetoxylating propylene with acetic acid in the presence of a palladium catalyst to form allyl acetate, hydrolyzing allyl acetate to form allyl alcohol, and then chlorinating it. In addition, Japanese Patent Application Laid-open No. 297333/1988 has suggested a method which comprises chlorinating acetone in the presence of an iodine chloride catalyst and a lithium chloride catalyst to form 1,3-dichloroacetone, and then reacting 1,3-dichloroacetone with isopropanol in the presence of an aluminum isopropoxide catalyst.
On the other hand, methods for preparing 3-chloro-1-propanol include a method in which a chloropropanol mixture obtained by treating 1,3-propanediol with hydrogen chloride is subjected to fractional distillation several times [Organic Synthesis Coll. Vol. 1, 533-534 (1964)], a method in which acrolein is reacted with hydrogen chloride in an alcohol to produce an acetal of 3-chloropropionaldehyde, and this acetal is then reduced in the presence of a ruthenium catalyst (Belgian Patent No. 634845), a method in which hydrogen chloride is added to acrolein to form 3-chloropropionaldehyde, and this is then reduced with an alkali metal borate (Japanese Patent Publication No. 42769/1977), and a method in which epichlorohydrin is reduced with zinc borohydride supported on silica gel to obtain a mixture of 3-chloro-1-propanol and propylene chlorohydrin [yield of 3-chloro-1-propanol=60%, J. C. S. Chem. Comm., p. 1334 (1990)].
However, in each of these methods, there are some problems such as the use of the prolonged manufacturing process because of requiring reactions in the several steps, the use of the expensive catalysts and the consumption of a large amount of chlorine for the chlorination of the raw material. Thus, a simple and economical method is desired.
As a method to solve these problems, the present inventors have suggested a method for preparing 2,3-dichloro-1-propanol and 3-chloro-1-propanol by irradiating methanol and 1,2-dichloroethane as starting materials with light in the presence of a peroxide and/or an azo compound (Japanese Patent Application No. 325516/ 1990), and a method for preparing 2,3-dichloro-1-propanol and 3-chloro-1-propanol by irradiating methanol and 1,2-dichloroethane as starting materials with light in the presence of a carbonyl compound (Japanese Patent Application No. 250700/1991).
These methods in which the reaction is caused to occur by the light irradiation can remarkably simplify the manufacturing process, as compared with a conventional method, but they have the following problems to be solved. That is to say, according to knowledge of the present inventors, in the method in which the light irradiation is done in the presence of the peroxide, the peroxide in an amount equimolar with methanol is required to produce a hydromethyl radical from methanol, and besides danger attends the handling of the peroxide. On the other hand, in the method in which the light irradiation is done in the presence of the azo compound and the method in which the light irradiation is done in the presence of the carbonyl compound, an improvement effect of activation is much lower than in the case of using the peroxide.